These examples highlight that many (at times strong) assumptions are necessary to reliably solve OPE tasks, particularly retrospective OPE tasks. Challenges of identifiability can be further complex if the corresponding estimand is individual-level and require estimating a complete probability distribution as opposed to expectations. For the most general dynamic data-generating processes, identifiability of the appropriate counterfactual estimands without parametric assumptions i.e. entirely based on the graphical structure has been outlined in [1]}.
